Acid-soluble concentrates of metal ores, ore concentrates and metallurgical intermediates can be leached or digested under pressure and at elevated temperatures in tube reactors.
For example, German patent document (printed application) No. DE-AS 19 37 392, discloses the pressure leaching of minerals, ores, or other materials by acid, alkaline or neutral aqueous medium in a tubular reactor utilizing a digestion tube.
In this system, a slurry of the material, hereinafter referred to as mineral material, is passed through the tubular reactor or digestion tube at a velocity of 0.5 to 7 meters per second and is treated in a turbulent flow with the leaching medium at temperatures up to and above 300.degree. C. in a comparatively short time.
This continuous-flow method has decided advantages over a batch method utilizing an autoclave and methods utilizing a cascade of autoclaves.
In spite of these significant advantages, problems are encountered, primarily when an acid medium is utilized as the lixiviant.
In this case, all of the tube surfaces traversed by the reaction mixture, including any heating tubes through which the acid-containing mixture passes, must be composed of material having a high resistance to acid. In earlier systems, therefore, even the mantles, jackets or shell tubes of heat exchangers had to be manufactured from such acid resistant material, greatly increasing the capital and replacement cost of the equipment and leading to a process which suffered from poor economy.
Maximum utilization of the energy in the earlier systems also could not be ensured.